<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style type="text/css">
*{
    padding: 0;
    margin: 0;

}
html,body{
    height: 100%;
}
#wrapper{
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0,3);
}
#p1{
    position: relative;
    top: 150px;
    width: 400px;
    height: 200px;
    text-align: center;
    line-height: 200px;
    margin: auto;
    background-color: white;
}
</style>
<body>
    <button id="btn">点我一下</button>
    <script>
        var oDiv=document.createElement('div');
        var oP=document.createElement('P');
        var oSpan=document.createElement('span');
        var bady=document.getElementById('btn');
        var bady=document.getElementsByTagName('body');
        btn.onclick=function(){
             oP.innerText='This is True music';
             oSpan.innerText='X';
             oDiv.id='wrapper';
             oP.id='span1';
             oSpan.id='span1';
             body[0].insertBefore(oDiv,btn);
        }
        oSpan.onclick=function(){
            body[0].removeChild(oDiv);
        }
    </script>
</body>
</html>